Automatic start circuit for lamp

ABSTRACT

An automatic start circuit for a gas-filled tube having an anode and a cathode, such as a deuterium lamp, the anode thereof being connected to both a voltage source for providing a firing voltage and a current source for providing the operating current after firing. The filament of the tube has a first voltage thereacross upon application of power to the circuit. A time delay circuit is provided having a time delay consistent with the warm-up time required for the tube, the termination of the predetermined time delay actuating a current regulator for regulating the anode to cathode current flowing through the tube. After the tube fires, the flow of such current energizes a filament voltage switch to apply across the filament a second voltage lower than the first voltage to compensate for power dissipation in the filament by virtue of the current flow. The time delay means includes an astable multivibrator providing pulses to a counter, which, after a preset count initiates a pulse to actuate the current regulator. The counter is reset by a reset circuit immediately upon application of power.

[ June 25, 1974 United States Patent [191 Diamond [57] ABSTRACT An automatic start circuit for a gas-filled tube having an anode and a cathode, such as a deuterium lamp,

1 AUTOMATIC START CIRCUIT FOR LAMP Inventor: Allen M. Diamond, Orange, Calif.

Assignee: Beckman Instruments, Inc.,

Fullerton Calif. the anode thereof being connected to both a voltage source for providing a firing voltage and a current Mar. 2, 1973 Filed! source for providing the operating current after firing.

The filament of the tube has a first voltage thereacross pp 0 upon application of power to the circuit. A time delay circuit is provided having a time delay consistent with the warm-up time required for the tube, the termina- 315/107, 315/171, 315/205, 3l5/D1G. 7 Int. Cl.

tion of the predetermined time delay actuating a current regulator for regulating the anode to cathode cur- [58] Field of Search............. 315/86, 101, 102, 107, 315/160, 171, 174-176, 205, DIG. 7

rent flowing through the tube. After the tube fires, the flow of such current energizes a fi switch to apply across the filament a lament voltage second voltage 1 References Cited lower than the first voltage to compensate for power UNITED STATES PATENTS dissipation in the filament by virtue of the current flow. The time delay means includes an astable multi- 3,568,004 3/1971 Parker............................ 315/102 X vibrator providing pulses to a counter, which, after a p i Examiner Herman Karl Saalbach preset count initiates a pulse to actuate the current Assistant Examinerlames B. Mullins regulator. The counter is reset by a reset circuit immediately upon application of power.

Attorney, Agem, 0r Firm-R. J. Steinmeyer; .1. G.

12 Claims, 1 Drawing Figure Mesaros CURRENT REGULATOR SW lTCH RESET CIRCUIT l l l I l 1 P l ASTABLE MULTl VIBRATOR AUTOMATIC START CIRCUIT FOR LAMP BACKGROUND OF THE INVENTION This invention relates to a start circuit for a gas filled lamp and more particularly to an automatic start circuit for a gas filled lamp having an anode and a cathode such as a deuterium lamp.

In typical gas filled lamps or tubes such as deuterium lamps a time delay is required for cathode warm-up, during which time it is desirable to apply to the filament a certain voltage which is higher than that necessary for continuous operation. Similarly with respect to such lamps the firing voltage, i.e. the voltage at which the lamp conducts between anode and cathode, can vary over a wide spread clue to the characteristics of the lamp. For example, in a deuterium lamp the firing voltage may vary from 125 to 350 volts while the on voltage at 300 milliamps varies between 40 and 100 volts. Another characteristic of a deuterium lamp is that the current required to lower the anode to cathode voltage below 125 volts is one to milliamps. Furthermore, start circuits for such lamp must have the capability to continuously reapply the firing voltage until the lamp fires. Due to the wide range of operating parameters of a gas filled lamp, start circuits that provide a firing voltage equal to the highest possible voltage to ensure that all lamps thereafter used fire, can result in excessive power and heat dissipation from the lamp after the lamp has fired. Similarly if an excess voltage is used on the filament to shorten the cathode warm-up time of a gas filled lamp, the excess voltage can shorten the lamp life as well as create excess heat.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention to provide a new and improved automatic start circuit for gas filled lamps or the like having an anode and a cathode.

It is another object of this invention to provide an automatic start circuit having time delay means for cathode warm-up of the gas filled lamp.

It is a further object of this invention to provide a regulated current through the lamp after the lamp has fired from a voltage lower than that necessary for lamp firing.

It is still another object of this invention to provide an automatic lowering of the filament power to compensate for the dissipation caused by the anode current.

It is a still further object of this invention to provide an automatic retiming of the time delay means to reinstitute application of the firing voltage after a power failure.

The foregoing and other objects of the invention are accomplished by providing a gas filled lamp having the filament or cathode thereof connected to a voltage source switchable between a first warm-up voltage and a second operating voltage, less than the first. The anode of the gas filled lamp is coupled to a voltage source for applying a firing voltage and then applying a current regulated low voltage after the lamp has fired. The current regulator is switched on after a predetermined time delay generally equal to the time required for cathode wann-up, the time delay being provided by the output of a counter to a latch after the count reaches a predetermined count. The clock pulses to the counter are generated by means of an astable multivibrator having a predetermined time constant so that the total number of pulses from the multivibrator to the counter provide an output from the counter equal to the time required for cathode warm-up. Reset means are provided to reset the counter immediately upon initiation of power to the circuit so that the predetermined time delay remains constant for each application of power.

Other objects, features and advantages of the invention will become apparent from the following specification taken in conjunction with the accompanying drawmg. I

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE is a schematic diagram of an automatic start circuit for a gas filled lamp in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Circuit Description Referring to the FIGURE there is shown an automatic start circuit for a gas filled lamp 10 having an anode 12 and a cathode or filament 14. Gas filled lamps such as deuterium lamps have particular application where a light source having a known light spectrum is desired, such as in spectrophotometry. However, one of the basic problems relating to such gas filled lamps, is that the operating parameters for such lamps vary from lamp to lamp within a given lot of lamps. For example the firing voltage can be anywhere within a range from 125 volts to 350 volts while the operating voltage to maintain conduction once the lamp has fired can be anywhere within the range from 40 volts to volts at 300 milliamps of operating current. Furthermore the current required to lower the anode to cathode voltage below volts can range anywhere between one and 10 milliamps. Gas filled lamps of this type further require a cathode warm-up time of 2.5 to 3 minutes to provide proper conduction once fired.

In the following discussion representative values of the following components will be given with respect to the operation of a deuterium lamp. Furthermore, major functional portions of the circuit have been enclosed in dotted lines and labeled with appropriate descriptions of the function for ease of explanation. These major functional elements include a filament voltage switch 16, a current regulator 18, a latch 20, an astable multivibrator 22, a reset circuit 24 and a counter 26.

The filament voltage switch 16 includes a NPN transistor 28 having the emitter thereof coupled to the negative side of a dc. source V which may be for example 13 volts do. The positive side of voltage source V is coupled to the filament 14 by'means of lead 29, with the other side of filament 14 being connected by means of lead 30 through a resistor 31 (20 ohms) to the base of transistor 28. The emitter of transistor 28 is connected to the collector thereof through resistor 32 (3 ohms), while the collector is also connected to the cathode of biasing diode 33, having the anode thereof connected to lead 30 intermediate resistor 31 and filament 14.

The anode 12 of lamp 10 is connected by means of lead 34 to first and second voltage sources. An altemating current source 35 (350 VAC) is applied through isolating transformer 36 when switch 37 is actuated to close the circuit between alternating current source 35 and the primary winding of transformer 36. The secondary winding of transformer 36 has one end thereof coupled to ground while the other end thereof is connected to the anode of diode 38, the cathode thereof being coupled through resistor 39 (15 K ohms) to lead 34. This provides a half wave rectified voltage through resistor 39. The second voltage source V 150 V.D.C.) has the positive side thereof coupled through diode 40 to lead 34.

The current regulator 18 includes an operational amplifier 42 and first and second NPN transistors 43 and 44, with the collector of transistor 44 being coupled by means of lead 45 to the base of transistor 28 of the filament voltage switch 16. The emitter of transistor 44 is connected to ground through resistor 46 ohms), the emitter also being connected by means of lead 47 through feedback resistor 48 (10 K ohms) to the negative input of operational amplifier 42. The output of operational amplifier 42 is coupled through resistor 49 (100 ohms) to the base of transistor 43, while the emitter thereof is connected to the anode of diode 50, the cathode of which is connected to the base of transistor .44, and also through resistor 51 (l K ohms) to ground.

The collector of transistor 43 is connected through bias resistor 52 (470 ohms) to a voltage source -l-V (l5 V.D.C.), this voltage source also providing the bias for operational amplifier 42 over lead 53. Lead 53 is coupled through power supply bypass capacitor 54 (0.01 microfarads) to ground. A negative source of bias V V.D.C.) is also applied to operational amplifier 42 by means of lead 55, which is similarly coupled to ground through power supply bypass capacitor 56 (0.1 microfarads).

Intermediate current regulator 18 and latch is a voltage divider including resistors60 (11.8 K ohms) and 61 (18.2 K ohms) connected in series between voltage source -V and lead 62 providing the output of latch 20. The point intermediate resistors 60 and 61 is connected to the positive input of operational amplifier 42.

The latch 20 includes PNP transistor 64 and NPN transistor 66, transistor 64 having the collector thereof coupled to lead 62 to provide the latch output. Lead 62 is also coupled to the base of transistor 66 through resistor 67 (3 K ohms). The emitter of transistor 64 is connected by means of lead 68 to a positive source of voltage +V the voltage source also being coupled to the collector of transistor 66 through series resistors 69 l K ohms) and 70 (3 K ohms). The point intermediate resistors 69 and 70 is coupled to the base of transistor 64. The emitter of transistor 66 is connected to ground by means of lead 71, while the base of transistor 66 is connected to ground through resistor 72 (l K ohms). The latch 20 is set by means of a pulse appearing at the output of counter 26, this pulse appearing on lead 75 through resistor 76 (l K ohms) through resistor 78 (.1 K ohms) to the base of transistor 66. The point intermediate resistors 76 and 78 is coupled through smoothing capacitor 79 (10 microfarads) to ground.

The input to counter 26 is provided by clock pulses appearing on lead 80 which is the output of astable multivibrator 22. The multivibrator 22 includes PNP transistor 82 and an NPN transistor 83, the collector of transistor 82 being coupled to the base of transistor 83. A capacitor 84 (100 microfarads) is connected between the emitter of transistor 82 and the emitter of transistor 83, the emitter of transistor 83 being connected to ground. The base of transistor 82 is connected to ground through resistor 85 (5.1 K ohms), while the base is also coupled to a voltage source +V (+5 V.D.C.) through series resistors 86 (1.6 K ohms) and 87 (l K ohms). The point intermediate resistors 86 and 87 is connected through resistor 88 to the emitter of transistor 82. This point is also connected to lead 80 and the collector of transistor 83.

A reset circuit 24 provides a reset pulse on lead 90 to reset counter 26 to zero. Reset circuit 24 includes a PNP transistor 92 having the emitter thereof coupled to a voltage source +V and the base thereof coupled to the same voltage source through resistor 93 (10 K ohms). The base of transistor 92 is connected through resistor 94 (l K ohms) in series with capacitor 95 (10 microfarads) to ground. The collector of transistor 92 is coupled to lead 90 and also coupled through resistor 96 (220 ohms) to ground.

Circuit Operation When power is applied to the circuit all voltages are energized simultaneously along with the simultaneous actuation of switch 37 to connect alternating current source 35 to the primary of transformer 36. The voltage sources then remain energized during the operation of the circuit.

Briefly, the operation of the circuit is as follows. With the initial application of voltage the reset circuit 24 provides a pulse on lead 90 to reset the counter 26. The astable multivibrator 22 and counter 26 form a time delay circuit which provides a pulse output on lead 75 at the expiration of a predetermined time period. During this predetermined time period the anode 12 of gas filled tube 10 receives its firing voltage on lead 34 from a combination of the half wave rectified alternating current voltage and the dc voltage source +V. (approximately 400 volts peak). Current to the filament 14 is being applied from a voltage potential of approximately 12 volts across the filament from the voltage source V through the filament 14, through lead 30, through resistor 31, through the base emitter path of transistor 28 to the negative side of voltage source V After the counter 26 achieves its preset count indicative of the predetermined time delay the pulse appearing on lead 75 sets latch 20, which, as will hereinafter be explained, remains set so long as the voltage sources are energized. With latch 20 set, a potential ap pears across voltage divider resistors 60 and 61 thereby providing a reference voltage to operational amplifier 42 of current regulator 18. After the current regulator 18 turns on, current flows from the anode 12 to the cathode or filament 14 of the gas filled tube 10. This Y asmuch as this sequence is controlled by the current through the lamp 10 rather than by the time delay means, the power to filament 14 will stay high until the lamp fires. Once the lamp 10 fires, the operating current (approximately 300 milliamps) is supplied from the low voltage power supply +V, (approximately volts) through diode 40 with a minimal amount of current being supplied from alternating current source 35 due to the high resistive value of current limiting resistor 39 K ohms).

Referring now to the reset circuit 24, the purpose of the reset circuit is to ensure that the counter 26 starts in the zero state, inasmuch as in the event of power failure counter 26 can be in any state when power is applied if it is not reset. When voltage source +V, is initially applied, capacitor 95 is discharged. Current then flows through the emitter to base junction of transistor 92 through resistor 94 to charge capacitor 95. This current turns on transistor 92, applying voltage to lead 90. This voltage sets the counter 26 to the zero state. As capacitor 95 charges, the voltage across it increases. When the voltage increases to the point that sufficient current can be supplied through resistor 93 to finish the charge and hold it, transistor 92 turns off. Resistor 96 then pulls the voltage on lead 90 down below the threshold of the reset input of counter 26. Resistor 96 must be small enough to hold the voltage thereacross below 0.7 volts.

With the counter 26 reset, the time delay means then proceeds for a predetermined time period equivalent to the desired warm-up time of the lamp 10. For a deuterium lamp 10 the desired warm-up time is 2.50 to 3 minutes or approximately 200 seconds. Due to the difficulty of building circuits with long time constants, pulse counting from an astable multivibrator is provided. in this manner no gating is required, and although the counter 26 is shown as a single counter, two decade counters can be used with the 8-binary output of the second decade counter being utilized to provide the output on lead 75. This would result in 80 counts of the multivibrator 22, which would effectively give a repetition rate of 2.5 seconds for the multivibrator 22 to achieve the 200 second time delay desired. In the astable multivibrator 22 resistors 86 and 85 supply the bias voltage for the base of transistor 82. Resistor 88 and capacitor 84 form the RC time constant that determines the frequency. Resistor 87 is the load resistor for transistor 83, and with the circuit off, very little current flows through resistor 87 thereby causing the voltage on lead 80 (the collector of transistor 83) to be approximately equal to the voltage source +V,. Current flows through resistor 88 to thereby charge capacitor 84. When the voltage on capacitor 84 rises to about 0.7 volts above the bias voltage supplied by resistors 85 and 86, transistor 82 conducts, thereby causing current flowing through transistor 82 to flow into the base of transistor 83, thereby turning on transistor 83. At such time as transistor 83 conducts, the voltage on lead 80 will be approximately equal to ground potential (with negligible voltage drop across the collector to emitter junction of transistor 83). Additional feedback through resistor 86 to the base of transistor 82 will hold transistor 82 in conduction until capacitor 84 is discharged through the emitter of transistor 82. As the capacitor 84 discharges the base potential of transistor 82 will drop below that necessary to sustain conduction, at which point transistor 82 will turn off thereby causing transistor 83 to turn off, letting lead 80 go back to its initial state of approximately the same potential as the voltage source +V,.

The pulses from astable multivibrator 22 continue until counter 26 reaches the predetermined count (80 counts) at which point lead 75 goes high."

Latch 20, immediately upon the application of power, is in the off condition with resistor69 preventing transistor 64 from conducting while resistor 72 prevents transistor 66 from conducting. When the pulse appears on lead 75 current flows through resistors 76,78 and 72 to ground. Resistor 76 and capacitor 79 form a transient filter to prevent premature firing when the power is applied or by noise spikes that could appear in the system. With the flow of this current a voltage appears across resistor 72, and when this voltage is greater than the base to emitter voltage drop of transistor 66, transistor 66 conducts, causing current to flow through resistors 69 and 70. The current flow through resistor 69 is sufficient to cause a voltage drop thereacross, thereby rendering transistor 64 conductive. The current flowing from the voltage source +V through the emitter to collector junction of transistor 64 through series resistors 67 and 72 to ground supplies a sufficient signal to maintain the conductive state of transistor 66 after the pulse appearing on lead 75 ends. Latch 20 remains latched until the power is subsequently removed.

Current flowing through the emitter to collector junction of transistor 64 from the voltage +V also flows through lead 62 and through series resistors 60 and 61 to a negative source of potential V The voltage divider consisting of resistors 60 and 61 is utilized to provide a reference voltage from the intermediate point between the resistors to the positive input of operational amplifier 42.

With respect to the current regulator 18, the basic circuit is a voltage follower, that is, the voltage at the emitter of transistor 44 will approximately equal the voltage at the junction of resistors 60 and 61. Resistor 49 is a current limiting resistor to limit the current output from operational amplifier 42 to the base of transistor 43. Transistor 43 functions as an emitter follower to give current amplification to the current flowing through resistor 49. Diode 50 is a protection diode to prevent high voltage from being applied back through resistor 43 into the voltage source +V in the event transistor 44 should fail. Resistor 52 is a current limiting resistor to protect transistor 43, with resistor 51 being a base bias resistor for transistor 44. When a positive voltage is applied from the junction of resistors 60 and 61 to the amplifier 42, the output of amplifier 42 goes positive, thereby applying a positive voltage to the base of transistor 43 rendering transistor 43 conductive, permitting current flow from voltage source +V through resistor 52, through the collector to the emitter junction of transistor 43, through diode 50, through resistor 51 to ground. This current flow will cause a voltage drop across resistor 51 sufficient to render transistor 44 conductive. At this point the anode to cathode current is flowing through gas filled lamp 10, the current flowing through lead 30, through resistor 31, through lead 45, through the collector to emitter junction of transistor 44 and through resistor 46 to ground. The current from amplifier 42 through resistor 49 will increase until the voltage drop across resistor 46 is approximately equal to the voltage applied to the positive input of amplifier 42. The voltage appearing at the emitter of transistor 44 is applied through current limiting resistor 48 to the inverted input of amplifier 42 to provide negative feedback thereby regulating the current through current regulator 18.

With reference to the filament voltage switch 16, as transistor 44 conducts and current flows through gas filled lamp 10 from the anode 12 to cathode l4, transistor 28 which was initially conductive now becomes nonconductive by the back-bias resulting from the current flowing through resistor 31 through transistor 34, through resistor 46 to ground. Transistor 28 then becomes rionconductive resulting in the flow of current to the filament from the positive side of voltage source V through lead 29, through filament 14, through lead 30, through biasing diode 33, through resistor 32' to the negative side of voltage source V In this manner the filament voltage switch 16, upon initial application of power, provides a first current path for filament 14 through transistor 28, and upon energization of current regulator 18 after the predetermined time delay resulting from multivibrator 22 and counter 26, provides a second current path through resistor 32 when transistor 28 becomes nonconductive. The net efiect is approximately 12 volts initially applied to filament 14, with approximately 10 volts being applied across filament 14 after the lamp has fired.

Consequently it can be seen by the utilization of the circuitry shown in conjunction with a gas filled lamp, the following functions are performed. A time delay is provided consistent with the required cathode warm-up time for gas filled lamps. By the utilization of a halfwave rectified alternating current voltage source in conjunction with a low voltage current regulated current source, two effects are achieved the firing voltage is continuously reapplied until the lamp fires, and the anode to cathode current of the gas filled lamp 10 is regulated from a low voltage power source after the lamp has fired. Furthermore with respect to the filament power, by providing two discrete levels of current therethrough, the filament power is automatically lowered after the lamp has fired to compensate for the dissipation caused by the anode to cathode current through the gas filled lamp 10. With the utilization of the reset circuit 24 the time delay means are automatically reset to zero in the event of a power failure.

While there has been shown and described a preferred embodiment, it is to be understood that various other adaptations and modifications may be made within the spirit and scope of the invention.

I claim:

I. In a circuit for starting and operating a gas-filled tube or the like having an anode and a cathode with a predetermined warm-up time, the combination comprising:

a voltage source connected to the anode for providing a firing voltage for said tube;

a current source connected to the anode for providing an operating current for said tube after conduction at approximately the operating voltage of said tube;

means for providing a first filament voltage to the filament of said tube;

current control means for controlling the current through said tube after firing;

time delay means for providing a predetermined time delay approximately equal to the warm-up time of said tube;

means responsive to the termination of said time delay for energizing said current control means; and

means responsive to the flow of current through said tube after firing for applying a second filament voltage lower than said first filament voltage during conduction of said tube;

2. The combination according to claim 1 wherein said time delay means includes a counter receiving timed pulses, a predetermined count initiating a pulse indicative of the termination of said predetermined time delay.

3. The combination according to claim 2 wherein said timed pulses are provided to said counter from an astable multivibrator.

4. The combination according to claim 3 wherein said time delay means further includes a reset circuit operable in response to the initiation of power to the automatic start circuit for providing a reset pulse to said counter.

5. The combination according to claim 4 wherein said means responsive to the termination of said time delay includes a latch circuit operative in response to the pulse output of said counter after the predetermined count, said latch circuit remaining set so long as power is supplied to the automatic start circuit.

said tube for applying a second filament voltage includes a voltage source switchable between said first and second filament voltages.

9. The combination according to claim 8 wherein said switchable voltage source includes a normally conductive switch in series therewith and a voltage dropping resistor in parallel with said switch.

10. The combination according to claim 9 wherein said switch is a transistor which becomes reverse biased and nonconductive upon conduction of current through said tube.

11. The combination according to claim 1 wherein said means responsive to the flow of current through said tube for applying a second filament voltage includes a voltage source in series with said filament and further in series with a normally conductive switch, said switch having a voltage dropping resistor in parallel therewith.

12. The combination according to claim 11 wherein said switch is a transistor, said transistor becoming reverse biased to render it nonconductive in response to the fiow of current through said tube only after said tube fires. 

1. In a circuit for starting and operating a gas-filled tube or the like having an anode and a cathode with a predetermined warmup time, the combination comprising: a voltage source connected to the anode for providing a firing voltage for said tube; a current source connected to the anode for providing an operating current for said tube after conduction at approximately the operating voltage of said tube; means for providing a first filament voltage to the filament of said tube; current control means for controlling the current through said tube after firing; time delay means for providing a predetermined time delay approximately equal to the warm-up time of said tube; means responsive to the termination of said time delay for energizing said current control means; and means responsive to the flow of current through said tube after firing for applying a second filament voltage lower than said first filament voltage during conduction of said tube.
 2. The combination according to claim 1 wherein said time delay means includes a counter receiving timed pulses, a predetermined count initiating a pulse indicative of the termination of said predetermined time delay.
 3. The combination according to claim 2 wherein said timed pulses are provided to said counter from an astable multivibrator.
 4. The combination according to claim 3 wherein said time delay means further includes a reset circuit operable in response to the initiation of power to the automatic start circuit for providing a reset pulse to said counter.
 5. The combination according to claim 4 wherein said means responsive to the termination of said time delay includes a latch circuit operative in response to the pulse output of said counter after the predetermined count, said latch circuit remaining set so long as power is supplied to the automatic start circuit.
 6. The combination according to claim 5 wherein said current control means is a current regulator.
 7. The combination according to claim 6 wherein the setting of said latch circuit supplies a reference potential to said current regulator.
 8. The combination according to claim 7 wherein said means responsive to the flow of current through said tube for applying a second filament voltage includes a voltage source switchable between said first and second filament voltages.
 9. The combination according to claim 8 wherein said switchable voltage source includes a normally conductive switch in series therewith and a voltage dropping resistor in parallel with said switch.
 10. The combination according to claim 9 wherein said switch is a transistor which becomes reverse biased and nonconductive upon conduction of current through said tube.
 11. The combination according to claim 1 wherein said means responsive to the flow of current through said tube for applying a second filament voltage includes a voltage source in series with said filament and further in series with a normally conductive switch, said switch having a voltage dropping resistor in parallel therewith.
 12. The combination according to claim 11 wherein said switch is a transistor, said transistor becoming reverse biased to render it nonconductive in response to the flow of current through said tube only after said tube fires. 